Tray Calculations

Two types of calculations may be performed: rating calculations for existing columns and sizing calculations for new columns.

Tray Rating

This option is used to determine the performance of trays in columns for which the tray details are known. Performance is measured in terms of the approach to flooding or flooding factor and the backup of liquid in the tray downcomers. Tray details must be provided, including the type of tray, diameter, spacing, number of passes, downcomer details, etc. See Column Tray Rating for further information on tray input.

Tray rating calculations are performed using the GLITSCH1 valve tray calculation method. For sieve and bubble cap calculations the valve tray results are derated by five and twenty percent, respectively. Specific tray hydraulic data for sieve trays and bubble cap trays are taken from the Design of Equilibrium Stage Processes by B.D. Smith.2

Within each section of trays, all trays are considered to be identical. Each section is rated independently of every other section.

Tray Sizing

The same methods used for tray rating calculations are used for tray sizing calculations. Sizing criteria include minimum tray diameter, tray spacing, maximum flooding factor and number of flow paths. See Column Tray Sizing for further details.

Sizing is used to calculate the diameter of each tray to meet the specified flooding criteria. Each tray within a section of trays is sized independently. The entire section is then re-rated, using the largest required standard tray diameter in the section.

Multiple sections of trays may be defined to provide for different diameters, tray spacings or other tray details within the column. Every section of trays is sized independently of every other section of trays.

Additional Information

All tray calculations require actual (flowing) densities for the liquids and vapors. These data must be provided for non-library, non-petroleum components. In addition, sieve tray calculations require viscosity data for the tray liquids and vapors. Therefore, a transport property method must be chosen for the simulation when sieve trays are used and viscosity data supplied for non-library, non-petroleum components.

References

1 Koch-Glitsch, LP, Ballast Tray Design Manual, Bulletin No. 4900, 3rd Edition.

2 Smith, B.D., Design of Equilibrium Stage Processes, Chapter 15 - Tray Hydraulics: Perforated Trays, McGraw-Hill (1963).